Imaging information acquired via various imaging modalities (e.g., X-ray computed tomography (CT), positron emission tomography (PET), magnetic resonance imaging (MRI), ultrasound, single photon emission computed tomography (SPECT)) may be combined. It may be desirable to generate complementary imaging data using two or more modalities to take advantage of unique benefits provided by each modality. For example, in some applications, it may desirable to combine complementary CT and MRI imaging information to analyze structures and/or functions from information provided by each modality.
For some imaging applications, for example neural and orthopedic imaging, concurrent or simultaneous acquisition of CT and MRI data is not essential. As such, a patient can be scanned on a CT system and then repositioned for acquisition of MRI data. For example, the patient's anatomy to be scanned may be immobilized and a table registered in both coordinate systems (namely, CT and MR coordinate systems) would be used to facilitate anatomical alignment. Alternatively, rigid and non-rigid motion estimation and correction techniques could be used to register the data. However, patient or organ motion during scanning or collection of imaging data may provide challenges to combining sequentially-acquired CT and MRI information. As one example, cardiac imaging (e.g., imaging of a beating heart) may be subject to motion of the heart during imaging. One conventional approach to minimize effects of a beating heart (or other motion) during CT scanning is to minimize the rotational time (or increase the rotational speed) of CT scanning equipment. However, as rotational speeds increase (and collection time decreases), image quality (e.g., signal-to-noise ratio) may decrease unless higher X-ray flux is provided by the X-ray tube. Further, challenges resulting from motion when imaging in a single modality may be exacerbated when combining sequentially-acquired imaging data from the complementary imaging modalities, as the motion or position of an object being imaged (e.g., the heart) may vary between the different times of imaging using the different modalities.